In many technical and industrial operations strong aqueous acid solutions are employed. In such operations, these acid solutions come in contact with metal surfaces which are thus subjected to corrosive attack by the acids. The problem is particularly prevalent in oil drilling operations, wherein with decreasing oil reserves it becomes necessary to drill deeper and deeper wells to obtain desired oil recovery. A common practice employed for enhancing drilling through sandstone and other rock formations, is to pump an aqueous acid solution down the well shaft through the rock formation to dissolve mineral constituents. Aqueous hydrochloric acid of about 15% concentration has been used for this purpose, but such acid is much too corrosive to be permitted to come in contact with carbon steel pipe and various chemicals have been added to the acid solutions to reduce their rate of attack on metals. Among the types of compounds found suitable to inhibit corrosion of metals by hydrochloric acid are aliphatic and cyclic amines, and certain unsaturated alcohols.
As deeper wells are drilled, with increasing temperatures thereby encountered, the rate of corrosion of the steel pipe is increased. To overcome this increased corrosion of the steel by aqueous hydrochloric acid solutions other acids have been used to replace all or part of the hydrochloric acid, such as formic acid. But as still deeper wells are required to be drilled even the reduced corrosive power of formic acid increases to such an extent that the value of the recovered petroleum does not compensate for increased loss of pipe due to corrosion.
Formic acid alone, although not as strong as hydrochloric acid, is corrosive to carbon steel and, especially in compositions including both formic and hydrochloric acid, it is necessary to add certain chemicals to these acid compositions to inhibit or reduce the rate of metal corrosion thereby. Many of the chemical additives which are effective in reducing metal corrosion by hydrochloric acid have also been found effective as corrosion inhibitors in formic acid solutions or mixtures of hydrochloric and formic acid. On the other hand, some of the most effective additives for reducing the corrosion of metals by hydrochloric acid, surprisingly, were found to be less effective as inhibitors in aqueous acid solutions containing formic acid in addition to hydrochloric acid.
In addition to well drilling, there are industrial operations in which strong aqueous acid solutions are employed in contact with metals subject to corrosive attack, including the field of metal fabrication where it is common practice to utilize such acid solutions in metal cleaning or pickling, for example, to remove surface oxide coatings prior to further processing, and in general for protection of storage tanks and pipelines against acid corrosion.
The patent and technical literature discloses numerous multicomponent formulations for inhibiting attack of ferrous or other heavy metals by corrosive acids. Such formulations include one or more components such as acetylenic alcohols, quaternary derivatives of heterocyclic nitrogen bases, halomethylated aromatic compounds, formamides and the like.
U.S. Pat. No. 3,634,270 proposes as a corrosion inhibitor a composition comprising (1) the reaction product of a selected amino compound with a ketone, an aldehyde and formic acid in ethylene glycol; in admixture with a (2) surface active agent such as an alkylphenoxy polyethoxy ethanol; and (3) a sulfur compound which may be a thiourea, thiocyanate or thiazole; and which composition may further include (4) an acetylenic alcohol.
In U.S. Pat. No. 4,028,268 multicomponent inhibitor compositions are described to be effective in protection of oil field tubular goods against attack by hydrochloric acid or other corrosive acids at elevated temperatures. The disclosed compositions comprise at least four specifically selected components:
(1) quaternary derivatives of quinoline (or other similar heterocyclic nitrogen bases) and a halomethylated polynuclear aromatic compound (e.g. polystyrene); PA0 (2) an acetylenic aliphatic alcohol; PA0 (3) a nonionic surface active agent, preferably an ethylene oxide adduct of a primary amine; which may be supplemented with a lauryl alcohol derivative of ethylene oxide; and PA0 (4) an ester or amide derivative of formic acid.